The present invention relates to a switching device for optional connection of a number of incoming electrical lines with a number of outgoing electrical lines such as for handling of telephone lines in access networks.
Several different designs of matrix crosspoint switching devices are known and have been used for different applications. Matrix crosspoint switching devices are generally designed with a plurality of incoming conductors and a plurality of outgoing conductors, where they form a matrix with a plurality of crosspoints.
In networks such as for example telephony it is desired to have automatic, remotely controlled crosspoint switches in order to connect cables in for example buildings and distribution cabinets. As regards telephone stations there is also a desire to have automatic switching between different types of service units and for connecting telephone subscribers.
A type of matrix crosspoint switching device utilising balls as contact elements at the crosspoints is disclosed in U.S. Pat. No. 4,954,674. The device comprises a connection block with a plurality of cavities containing crosspoints of the plurality of contact pairs, where each cavity comprises an electrically conductive ball and an electrically insulating ball. The balls are positioned such as to provide electrical contact or no electrical contact between incoming conductor pairs in one direction and outgoing conductor pairs in the outgoing direction with the aid of operating rods which transmit the operating force from one connection site to an adjacent operating site.
The device according to U.S. Pat. No. 4,954,674 significantly reduces the size of a crosspoint matrix switching device in contrast to the conventional mechanical relaying devices. However it comprises a large number of elements that are movable with respect to contact surfaces and to each other, which complicates the manufacture of the device. It is further not an ideal solution as regards flexibility and size in view of the increasing demands on reducing the size, i e packing density, and high flexibility. A matrix switching device is needed that fulfils these demands and is, inexpensive.
The object of the present invention is to provide a switching device capable of optionally connecting a number of incoming electrical lines with a number of outgoing electrical lines in a way that is space saving, flexible and inexpensive.
The benefits of the present invention are several. By arranging electrical contact surfaces on a cylindrical surface, which contact surfaces are electrically connected to the incoming and outgoing electrical lines, and by providing an axially symmetrical rotatable body adjacent said cylindrical arranged with contact elements, it is possible to provide electrical contact between selected incoming lines and selected outgoing lines by rotating the symmetrical body. Because the whole circumference, i e 360xc2x0, of the cylindrical surface may be used, it may be divided into a large number of contact points, thereby providing a large number of crosspoints between the incoming and outgoing lines. The contact surfaces may also be divided in the longitudinal direction of the cylindrical surface, facilitating the arrangement of the crosspoints in that the contact surfaces of the incoming lines are arranged over or under the contact surfaces of the outgoing lines as seen in the longitudinal direction, and designing the contact elements so that they are capable of bridging the gap between selected contact surfaces of the incoming lines with selected contact surfaces of the outgoing lines.
The benefits of the present invention are several. By arranging electrical contact surfaces on a cylindrical surface, which contact surfaces are electrically connected to the incoming and outgoing electrical lines, and by providing an axially symmetrical rotatable body adjacent said cylindrical arranged with contact elements, it is possible to provide electrical contact between selected incoming lines and selected outgoing lines by rotating the symmetrical body. Because the whole circumference, i e 360xc2x0, of the cylindrical surface may be used it may be divided into a large number of contact points, thereby providing a large number of crosspoints between the incoming and outgoing lines. The contact surfaces may also be divided in the longitudinal direction of the cylindrical surface, facilitating the arrangement of the crosspoints in that the contact surfaces of the incoming lines are arranged over or under the contact surfaces of the outgoing lines as seen in the longitudinal direction, and designing the contact elements so that they are capable of bridging the gap between selected contact surfaces of the incoming lines with selected contact surfaces of the outgoing lines.
The design of the switching unit according to the invention provides a very compact solution. The symmetrical body is preferably driven by an electric motor, and more preferably by a stepper motor, which enables and facilitates the use of a plurality of contact points around the circumference of the cylindrical surface. The solution requires very little power consumption for the switching, and no power consumption when in the required contact position.
As an alternative design, the switching unit may be arranged such that the contact surfaces and contact points are arranged on a plane, for example a circuit board, in concentric rings or areas, that a drive means is arranged in the center of the rings and that contact elements are arranged by the drive means such that they provide a bridge between the contact surfaces and selected contact points.
The switching unit is further preferably provided with position signalling means, enabling a precise knowledge of the rotational position of the symmetrical body in relation to the cylindrical surface, and thus the crosspoints of the lines. The switching unit may further be provided with a home or reference position and memory means for storing the number of steps that the unit has moved.
The switching unit according to the invention may also be connected to further switching units, which greatly enhances the flexibility of the switching device. Preferably either the incoming or the outgoing lines are connected through all switching units and a set of outgoing or incoming lines respectively are arranged to a respective switching unit thereby providing a matrix crosspoint switching device, where each switching device is arranged with its own drive means for selectively connecting its set of lines with the through-going lines.
The sizes of the drive means available today enables a very compact design of the switching units, in the order of 20xc3x9720xc3x9710 mm for each unit. Preferably one unit or several interconnected units are connected to a printed circuit board comprising the necessary control means for activating the motors and to position the symmetrical body in order to obtain the required contacts between the incoming and outgoing lines. Further, if several switching units are interconnected, a connection block is arranged for directing the lines down to the circuit board, thereby reducing the wiring and facilitating the design and layout of the circuit board.
Further aspects of the present invention and advantages with it will become apparent from the following detailed description of the invention and from the accompanying drawings.